Factory employees since the date of entry into the factory according to the labor law how long must sign a contract and buy social security.

The employer shall sign a written labor contract with the worker within one month of the worker's entry into the job; the employer shall apply for social security procedures for the worker and buy his social security from the date of his entry into the job.

Legal basis of the People's Republic of China Labor Contract Law

Article 82 If an employer fails to conclude a written labor contract with a worker for more than one month but less than one year from the date of employment, the employer shall pay the worker two times his/her monthly wages.

If an employer violates the provisions of this Law by failing to conclude an open-ended labor contract with a worker, the employer shall pay the worker two times his or her monthly wages from the date when the open-ended labor contract should have been concluded.

The employer shall fulfill the obligation to pay social insurance for the workers in a timely manner according to the law. Employers and workers to establish a labor relationship that from the date of employment within thirty days of the social insurance agency for workers to apply for social insurance registration procedures. The employer shall pay the social insurance fees in full and on time after self-declaration, and shall not postpone or reduce the payment except for force majeure and other legal reasons. If the employer fails to pay the social insurance fees on time, the social insurance collection agency shall order the employer to pay the fees within a certain period of time, or to make up the full amount of the fees. If the employer fails to pay or make up the social security premiums after the deadline, the social security collection agency may inquire the bank account from the bank or its bank and may apply to the administrative department at or above the county level to make a transfer of social security premiums. Employer account balance is less than should pay social insurance premiums, social security collection agency, may require the employer to provide security, sign an agreement to defer payment.